Cutting Tools for CAM – Part 4
Heat – how it occurs, where it goes, and how it can be either advantageous or detrimental is one of the most widely misunderstood aspects of machining. Shops intent on increasing machining efficiency should devote some time to better understanding the positive and negative attributes of heat.
Some materials absorb heat and others resist it. When a material like steel absorbs heat, it softens to a near liquid state, the part can be cut like butter, and the heat is removed from the process and the tool and transferred to the chips. In this case heat is very beneficial and allows ultra-high material removal rates with appropriate tools in combination with dynamic tool motion. Machining can be and usually should be performed without coolant. In this case coolant-free cutting is better because it eliminates the thermal cycling caused by the intermittent exposure of coolant to the rotating flutes, and the tool lasts longer. Blowing the cut with air is desirable, not for cooling, but to clear the chips away from the process.
On the other hand, superalloys such as Inconel are heat resistant. They absorb so little heat that what is not flushed away by the coolant remains at the tool/material interface or, even worse, absorbed into the tool. This can cause all sorts of problems. Temperatures up to 1300°C can create wear, plastic tool deformation, and delimitation of the tool’s protective coating.
Some shops attempt to combat this challenge by reducing depth of cut to minimize heat generation. This strategy is counterproductive because it makes the chips even smaller, further reducing their heat removal capacity while it retards the cutting efficiency.
Taking deep cuts in superalloys is generally a more efficient approach but this strategy can create significant pressure increases on the tool as it becomes duller, progressively increasing the danger of breakage. This danger can be ameliorated by use of dynamic motion technology, which adjusts the tool motion based on material conditions ahead of the cut to compensate for excessive forces that can be generated.
The important takeaway points of this discussion:
- Machining steel at high temperatures using the right tools and toolpaths can result in exceptional productivity improvements. (See radial chip thinning discussion in our next article.)
- It is very important to manage heat during processes for cutting superalloys to minimize tool breakage, tool wear and damage, and part damage. Shops machining these materials should develop a close working relationship with their tool supplier to optimize their superalloy cutting strategies and compensate for excessive forces that can be generated based on material conditions ahead of the cut.